In many types of electrical systems and notably in motor vehicles, there is little standardization of signals. A prime example of the lack of standardization is the fact that many motor vehicles use an external (to the item being controlled) signal source such as switches in the ground circuit while others use switches in the "hot" (+12V) circuit. In some cases, for convenience, a single vehicle may have both switched hot and ground signals. Without limiting the generality of the present invention, all references hereinafter will be to a motor vehicle system, it being understood that the invention as claimed will find use in many other applications.
It is often desirable to have a universal control or other electrical system which can be used in motor vehicles regardless of the nature of the signals available therein. Such universality has not been found in the known prior art and various compromises have therefore had to be made. Additionally at least certain of the prior art devices are not fail safe in the event of an incorrect connection from an external signal.
It is therefore an object of the invention to provide an interface means to allow an electronic control system or the like to be readily used with external signals of differing types, particularly with "hot" and "ground" signals.
It is another object to provide such a means which is fail safe in the event of an incorrect connection.
It is a further object of the invention to provide such an interface in an extremely simple way.